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Motor microstepper translates into simpler designs

Posted: 13 Apr 2005 ?? ?Print Version ?Bookmark and Share

Keywords:allegro Microsystems? a3982? motor driver ic? driver ic?

Allegro MicroSystems' A3982 is a complete bipolar motor driver IC with input logic translator to simplify motor stepping and direction for basic office automation and industrial applications.

Users can advance the motor in full- or half-step increments. In general operation, this PWM-type device drives the motor one step for each input pulse. There are no phase sequence tables or high-frequency control lines, or complex interfaces for the designer to program. In the half-step mode, the current in each motor phase is switched between 100 percent current (one phase on), 70.7 percent (two phases on), and zero. Sequencing of the current in this manner results in the same torque produced in each step, and therefore more predicable operation.

The A3982's chopping control circuitry, which includes a fixed off-time output current regulator, automatically selects the current decay mode (slow or mixed). The A3982 determines if each step results in a higher or lower current in each of the motor phases. If the change is to a higher current, the decay mode is set to slow decay. If the change is to a lower current, then the decay mode is set to mixed decay with 31.25 percent fast and 68.75 percent slow decay. This scheme results in reduced audible noise, increased step accuracy and reduced power dissipation.

The chip's DMOS output stage (two full-bridge outputs) is rated at 35 volts and 1.5A (2A peak). Internal synchronous rectification control circuitry, along with the low on-resistance output stages, minimizes thermal management considerations. The synchronous design improves power dissipation by 20 percent or so; in addition, no external Schottky diodes are required. Internal circuit protection includes thermal shutdown with hysteresis, under-voltage lockout and crossover current protection.

The A3982SLB, manufactured using the company's ABCD (Allegro Bipolar CMOS DMOS) process, is offered in a 24-lead SOIC (15.4-by-7.5mm). It is priced at $1.80 each in 10,000-unit quantities. This controller is also available in a Pb-free version.

- Vincent Biancomano


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